This invention relates to radar or the art of detecting threats or threat signals from hostile sources or emitters and has particular relationship to the tracking of such signals. Typically this invention concerns itself with a pulse-repetition-interval (herein referred to as PRI) trackers. A PRI tracker is apparatus that synchronizes with a received pulse train of a threat and generates a time-prediction parameter for each pulse in the train so that the tracker is locked to the pulse train. The tracker remains locked to the pulse train even if some of the pulses of the train are not received. This facility is called fly-wheeling.
Since trackers are used in regions which may be subject simultaneously to a number of threats, a number of trackers are demanded for the protection of any region. In accordance with the teachings of the prior art, separate trackers with separate track loops are used to detect the separate threats. Typically, prior-art PRI tracking involves hybrid digital/analog techniques which require significant quantities of hardware. Prior-art trackers have exhibited performance limitations when they encounter pulse trains which are staggered or jittered, or which contain more than an occasional missing pulse. The presence of multiple pulse trains that "walk through" each other also cause the prior-art trackers to unlock or transfer lock from one train to another. In addition to these shortcomings, the mechanizations of these trackers usually require a complete separate set of tracker hardware including a separate tracking loop for each pulse train to be tracked. The implementation of each tracker requires a significant number, usually 50 to 150 integrated circuits depending on complexity. To economize on integrated circuits and other parts, the number of trackers is minimized and usually there are fewer trackers then desired or even required. In addition, the trackers that are provided constitute a significant part of the power demand, size, and weight of the protective apparatus and present a significant part of the reliability and maintainability problems.
It is an object of this invention to overcome the above-described difficulties of the prior art and to provide for each protected region adequate tracking facilities with minimal integrated circuit demands, which facilities shall constitute only a reasonable or minor part of the power demand, size and weight and shall present only a reasonable part of the reliability and maintainability problems of the apparatus.
It is another object of this invention to overcome the hardware penalties imposed by multiple PRI tracking in prior-art apparatus and to improve tracker performance generally, and specifically with respect to pulse-train threat signals that are not well behaved. It is also an object of this invention to provide for the selection of the most logically proper of a plurality of pulses which appear in a prediction window and for the assignment of a window to the one of a plurality of pulses which has missed the window the most.